Radio receiving apparatus



July 23,1946 A; D. SM1-FH, JR

RADIO RECIEVIN'G APPARATUS Filed oct.v 19, 1945 qvbkb 92 -m e@ 1N V EN TOR.

Patented July 23,1946 2,404,408

l RADIO RECEIVING APPARATUS Y i `Archibald D. Smith, Jr., Amityville, N. Y., assign-` v or to Federal Telephone and Radio Corporation, A v um Y `New York,` N.Y.,:a corporation of Delaware,

. application october-19,194s,seria1No.50s,79s

' 1 Gentils. ((1250-20) fs",'lzrrr.s PATENT voI-Flclal f-'f This invention relates to improvements in amfier 22 (if desired) an thence to a suitable ref ,p lifiers, andmore particularly toia lnovel reflex` producer '23. amplifying system for radio receivers. The intermediate frequency amplifier I I, vac.,- I object of this invention is to provide a novel c'ordingv tothe present invention, may consist and'v improvedreflex amplifier. 5 ofi one or `more stages. YThe input tothe inter- Another object of'this invention is tol provide mediate frequency amplifier passes through vva a novel radio receiving circuit in which the high direct capacitative coupling device I2, while the frequency amplifier tubes serve to amplify the output fromthe intermediatefrequencyamplilow audio frequencies. fier consists of a similar coupling device,l as .does i A further object of this invention is to provide alsothe coupling between anyintermediate stages,

a reflex amplifier in which the lower audio fresuch as indicated lgenerally at I3. The ydirect ,quencies arepassed through and are amplified by capacitative coupling device in accordance with the radio frequency amplifier without mutual inthe present invention may consist of two inducterference. s -tors 24 and` 26 spaced apart sorthat there will s A still further object of thisinvention is to pro- Iloe no mutual coupling Vbetween them, the actual videa reex amplifier in vwhich the input, output coupling taking place through acommon conand inter-jstage couplingdevices'of the radio frenection which is connected to ground througha quency amplifier are adapted to pass both the common condenser v28. The inductors24 and `26 normal high frequencies and the low audio fremay be adjustable so that with their inherent ,quencies withoutgmutual interference. capacities C and C', together with the condenser Morespecifically, the present invention is di- 28, the circuit will be tuned tothe intermediate rected to the use .of direct capacitative `coupling frequency band desired. In this respect the cou- Vmeans in a radio frequencyamplifier which is also pling in the `intermediate frequency ampliferwill usedl to amplify reeXed .audio frequency currents. actin theusual manner. If the low audio fre- .An illustrative embodiment disclosing one form 25 quency is fed, however, to the midpoint between ,of l the invention together with a modied circuit `the two coils, `to which the `condenser 28 is con- 4detail thereof is shown in the accompanying nected, 'this point willI representan Vappreciable drawing in whiehg@A y impedance for low frequencies. At`suchlow fre- V .liig.; 1 is a circuit diagram, partially in block 'f quencies, however, the impedance oi the individform illustrating a preferred embodiment of the 30 ualcoils is negligible and the Coupling iS effeted present invention;and lsolely through thecapacitor 32.V For low fre- Fig. 2isa partial circuit diagram of a modified quency currents the capacitor 23 may be bycoupling device adapted to be used in the circuit passedbya variable resistor 30 to control the low shown in Fig. 1. frequency coupling characteristics, this resistor The present invention isdirected to improve- Sewing @t m6524111? "time 21S 21D- C- path fOl the ments in what are known in the art as reflex anodecurrent of theprevious high frequency or amplifiers, and in Fig. 1 I have illustrated by way miXer Stge. The type 0f Coupling deViCe d6- of example the application of my invention to a scribed, therefore, serves both as coupling means superheterodyne receiver. Such a circuit may OI the relatively high intermediate frequency consist of a first detector, mixer, local oscillator currents and also for the relatively low frequency and the like, indicated at IIl, the output of which audio currents which then are derived, preferis passed through an intermediate frequency amably from the last coupling device between the plifier, generally indicated at II, to a second deintermediate" frequency amplifier and the second tector I4. In accordance with the present invena detector I4. The low-pass filter 20 is used to tion the audio frequency output derived from the prevent passage of the high frequency currents detector I4 is fed back to the intermediate frefrom the output of the intermediate frequency quency amplifier I I through a de-coupling conamplifier to the audio frequency reproducer, While denser I6 and a low-pass filter I8. After the the low-pass filter I8 is used to prevent the high audio frequency currents pass through and are frequency currents derived from the input of the A:amplified by the intermediate frequency ampliintermediate frequency amplifier, being impressed fier in a manner to be described in more detail upon the detector circuit. In order to prevent the hereinafter, such amplified audio frequency outhigh plate voltages from being applied to the grid put is taken from the output of the, intermediate of the intermediate frequency amplifier tube 34, frequency amplifier, passed through another lowor to the input of the detector tube (not shown) pass filter 20 through an audio frequency ampli- 55 condensers 32 may be inserted between the inductor winding 26 and the common point connecting that inductor to the inductor 24 and the condenser 28.

In place of using an adjustable resistor 3U, the

condenser 28 may be'shunted by a variable in- Y ductor 40 and a resistor 42, as shown in Fig. 2. By propenadjustment lof the inductor 42, the over-all circuit for low-frequencies may be shunt peaked,'making the low frequency circuit have a flat band-pass characteristic. Other known forms of band-pass (low frequency) compensation could be used, if desired.

, While the present invention has the general add vantage of all reflex circuits in permitting thev r reduction of the number of required tubes, it hasj Vthe further advantage of permitting the use of several high frequency amplifyingstages as audio frequency stages by utilizing special coupling, 'means which will couple the amplier both for rhighandA low frequencies without mutual interference. l

:While I have disclosed this invention specifically in connection'with a superheterodyne receiver, it will be obvious to those skilled in this art that the invention is equally applicable to a multi-stage tuned radio frequency receiver.V

.no mutual inductance between the` coils. The

coils may be provided with variable movable powdered iron cores for tuning purposes, or they may be tuned in other manners known to the art.

Accordingly, while I have described above the principles of myginvention in connection with specific apparatus, together with a particular modification thereof, it is to be clearly understood that this description is made only by way of example and notas a limitation on the scope of my invention as set forth in the objects and the accompanying claims. I claim:V y

1. Radio receiving apparatus including, in combination, a high frequency amplifier having one o-r more relatively high frequency amplifying stages, each of said stages including input and output direct capacitative coupling' means, comprising a pair of uncoupled inductors having a common connection and a common condenser connecting said common connection :to ground, an

4 Y input circuit connected to said high frequency amplifier through the iirst said input coupling means,l a detector connected to the output coupling means of said high frequency'amplier,

means connecting the output circuit of saidV detector to the common connection of one of said input coupling means of an amplifying stage, a signal reproducing device, a low-frequency pass filter, and means connecting said signalr reproducing device to the common connection of an output'coupling means following said one input coupling means through said low-pass lter. I

2. The combination according tol claim 1, in combination with a second low-pass filter intermediate connected between the output of said detector and the said common connection of the linput coupling meansvto an amplifying stage.

3. The combination according to claim 1, in

combination with variable impedance means in shunt with the common condenser of each coupling means.l

4. The combination according` to claim 1, in Y which the inductors and common condenser of Y each coupling means are tuned to the said high frequency band, in combination Witha variable inductance in shunt with said common condenser l forming a ilat band-pass filter dimensioned to shunt peak the circuit for the low frequency detector output. f

5. The combinationraccording to claim: 1, in which the detector output is fed to the input coupling means of the rst high frequency am- I pliiier stage, and the signalreproducing device is connected to the output coupling means of the last amplifier stage. Y

' 6. Radio receiving apparatus including, in combination, a high frequency amplierhaving one or more relatively high frequency amplifying stages, each of said stages including input and output direct capacitativecoupling means, comprising a pair of uncoupled inductors having a common'connection and a common condenser connecting said common connection to ground, an input circuit connected to said high frequency Aamplifier through the rst said input coupling 

